Initial results from the JT-60 upgrade

The initial experimental results in the JT-60 (JAERI Tokamak-60) upgrade are reported along with an overview of reconstruction of JT-60 and future plans for the upgrade. Reconstruction of the JT-60 machine was successfully completed at the end of March 1991. 4-MA stable NB (neutral beam)-heated discharges with a discharge duration of 15 s and a flat-top duration of ~1 s have been achieved in a short operational period of 4 months. The stored energy has reached 5.1 MJ with I _P=4 MA, B_t=4 T, and NBI (neutral-beam injection) power of 20 MW. The global energy confinement time of 0.9 s has been achieved in deuterium OH discharges with I_P=3 MA, B_t=4 T, and n _e=2×10¹⁹ m^-3. The energy confinement time of 0.25 s has been achieved in 15-20-MW NB-heated deuterium plasmas with I_p=4 MA. The confinement time is in good agreement with that in the L-mode scaling of the ITER89 power law. The discharges of high ion temperature mode with T_i (0) over 20 keV have been obtained by injecting deuterium NB with low target density of ~0.5×10¹⁹ m^-3, where the maximum neutron yield is 1.3×10¹⁶ n/s and the energy confinement time is about 2.5 times as large as that of the International Thermonuclear Experimental Reactor power law scaling